The unlikely epicentre of Italian politics this week has been an elegant, book-lined study commanding stunning views over the Ligurian coast.

Sitting alone at the computer in his villa, high up on the hills outside Genoa, anti-graft comedian Beppe Grillo has been firing off blog entries that have dominated newspaper headlines and been dissected endlessly on chat shows.

No wonder, after candidates from his Five Star movement were elected mayors in three towns, including Parma, this week, taking his tally of mayors to four, while 163 supporters became councillors in a round of local elections that saw Silvio Berlusconi's Freedom People party all but wiped off the political map.

Then a poll this week put Grillo's nationwide support at 18.5%, making it the second political group in Italy, behind the centre left Democratic party but ahead of Berlusconi, the former prime minister who handed over the reins of power to technocrat Mario Monti in November.

"Berlusconi is so dead he doesn't even wear his makeup anymore," the tousle-haired comic told the Guardian.

Now, as he rides a Europe-wide wave of discontent against incumbent parties, Grillo says he is planning an online poll to find about 100 candidates for next year's national parliamentary elections.

"We are adding a percentage point in the polls every week as the mainstream parties die out," he said. "I am not sure who will be left to face us in parliament."

While Grillo refuses to appear on talkshows or give interviews to the Italian press, which in turn has done its best to ignore him, he has built his blog – backed by his caustic one-man show – into a formidable online campaign pushing green issues and battling corrupt politicians.

Lately he has also added an anti-austerity edge, attacking Monti's tax hikes and calling for Italy to drop out of the euro.

But his main target remains Italy's pampered political parties, whose popularity hit new lows when Berlusconi's former coalition partner, the Northern League, was accused of investing its election campaign subsidies in diamonds and gold ingots.

"We have a political class of kleptomaniacs that needs to put back what it has stolen, from their bank accounts to their lofts, and then, because we don't want them sneaking off to the Seychelles, be put before a jury," said Grillo.

It is no coincidence Grillo's first big win was Parma, where street protests last year helped oust the Berlusconi-backed mayor after he racked up a municipal debt estimated at €600m (£480m).

The first task facing new mayor Federico Pizzarotti, a 39-year-old IT manager, is to halt the construction of a rubbish incinerator deemed polluting by the Five Star movement, part of a green platform which also opposes Italy's creeping urbanisation and pushes electric cars and recycling. After slamming politicians, Grillo gets just as passionate discussing water saving toilets and solar panels.

As other European countries cast protest votes for anti-immigrant parties and neo-fascists, Grillo points out that Italy has settled for a comedian. "Italy invented fascism, yet it is us, boy scouts and students, filling the void," he said. "Everyone should thank us, because if we fail we will get the xenophobes."

Nor does he have much time for the Occupy movement. "They ended up battling the police, while we brought our protest inside the system with our candidates."

Furious, sweaty and loud on stage, Grillo is deceptively calm at home, raising his voice just once during lunch with his wife and two of his four children, before piping down on the advice of his teenage son.

The marble floored study from where he pounds out his venomous attacks on Italy's trembling politicians is hung with prints of orchids. Outside, a garden full of well trimmed rose bushes looks out over the Mediterranean.

The son of a Genoa welding torch salesman, Grillo has come a long way since he was kicked off Italian TV in the 1980s for poking fun at politicians.

The comic, 63, says he first used his blog in 2005 to help build his stage act, soliciting dirt on local politicians in towns he was due to perform in.

"Then we started writing about jobs and renewable energy, and we began to shape a programme based on comments from everyone, from Nobel prize-winners to my electrician." Along the way the blog became one of the ten most read in the world.

To allow readers to contact each other at a local level, Grillo copied the Meetup concept that 2004 US Democratic presidential contender Howard Dean had pioneered, spawning 250 groups in Italy which have now produced the movement's local political candidates. Grillo says he merely checks to see if they have criminal records or are already members of another party.

"It's hyperdemocracy – I still don't fully understand it. We'll understand it in five or six years."

With little publicity, he brought two million people on to the streets in 2007 for his Vaffanculo (Go fuck yourself) day of protest, garnering 350,000 signatures in favour of booting MPs with criminal records out of parliament.

The petition, which Grillo says "is still stuck in a drawer", also called for the scrapping of a 2005 electoral law which took away the right of voters to pick MPs, allowing parties to choose who goes to parliament.

That measure, more than any, may have fatally weakened Italy's loyalties to its traditional parties. And as Grillo constantly points out, the Five Star movement is not a party, and he will never be a candidate.

"When people call up and ask to speak to the party secretary I hand them my 12-year-old son," he says.

Lacking a rigid party structure, the challenge facing the movement is balancing the autonomy handed to candidates, against Grillo's leadership, and the Italian press is already sniffing around alleged frictions between the comic and Pizzarotti, something Grillo denies.

Things could get tougher next year as candidates for parliament get to grips with the movement's national manifesto. Grillo said it is "still in the works", but he is keen on nationalising utilities and even banks, as well as closing down Italy's tax debt collection agency.

What will draw votes is Grillo's pledge that his MPs will take a voluntary wage cut. "We will be setting rules on benefits, cars and hairdressers," said Grillo. "And they will be heading into parliament wearing helmets and holding webcams."